1. Field of the Invention
The present invention relates to an illumination apparatus which is assumed to be used mainly outdoors, such as a street light, a garden light, or a projector. Further, the invention relates to a light source module using, for example, a plurality of light emitting diodes as a light source.
2. Description of the Related Art
An illumination apparatus for outdoors, such as a street light which illuminates a sidewalk and a roadway, is attached to a high point of a pole mounted at the side of a road. The illumination apparatus for outdoors of this kind uses, for example, a fluorescent lamp or an HID lamp as a light source. In recent years, to realize energy saving and easier maintenance, an attempt is being made to use a light emitting diode as the light source for outdoor illumination apparatuses in place of a fluorescent lamp or an HID lamp.
As regards a street light for increasing a crime prevention effect, for example, appropriate illumination intensity according to location is suggested so that the shape, the face shape, and the like of a person can be identified. Specifically, it is recommended to set a street light whose horizontal illuminance (average value) is 3 lux and whose vertical illuminance (minimum value) is 0.5 lux as the brightness at which the crime prevention effect can be expected. Concurrently, it is also requested to reduce the cost of mounting a street light and economically obtain light distribution of a wide range by widening the mounting interval of street lights as much as possible.
To satisfy the request, for example, in an illumination device for outdoors disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2004-200102, a plurality of white light emitting diodes are used as a light source. This conventional illumination device for outdoors has a plurality of flat print boards on which the plurality of white light emitting diodes are mounted. The print board is attached to mounting hardware in an attitude such that the white light emitting diodes are directed downward and moreover in multiple directions.
However, a light emitting diode is a point source of light in which the shape of a light emitting part is small. Consequently, to obtain a luminous intensity distribution over a wide range by using light emitting diodes, a number of light emitting diodes have to be arranged. For this reason, a problem in cost occurs, the structure of the illumination device for outdoors is made more complex, and it cannot be avoided that the work of assembling the illumination device for outdoors becomes troublesome.
Therefore, if using a large number of light emitting diodes as a light source, how to arrive at an illumination device for outdoors which can distribute light over a wide range while simplifying the arrangement of light emitting diodes is an important issue.
Further, as regards a light emitting diode, despite the small shape of a light emitting part, the light intensity is high. Consequently, as disclosed in the Jpn. Pat. Appln. KOKAI publication, the light emitting part of the illumination device for outdoors using a number of light emitting diodes for illumination in multiple directions has a high brightness, which tends to produce glare to those looking at it.